Technical Field
The present disclosure relates to a syringe assembly including an outer barrel holding a puncture needle at its barrel tip, and a cap mounted detachably to the barrel tip; a method and an assembly device for assembling the syringe assembly; a pre-filled syringe using the syringe assembly; and a method for assembling the pre-filled syringe.
Background Art
As described in JP 2004-532060 W, in a pre-filled syringe preliminarily filled with a drug solution, a cap is mounted detachably to a barrel tip of an outer barrel provided with a puncture needle, for example. The cap mounted as described above protects the puncture needle, and seals a needle hole.
The cap is mounted before a plunger is inserted in a cylindrical space in the outer barrel or before a drug solution is filled in the outer barrel. A process of mounting the cap will specifically be described below.
A cap has a receiving hole for receiving a puncture needle. Firstly, a puncture needle is inserted into the receiving hole, and then, a barrel tip of an outer barrel is press-fitted to the receiving hole. In this case, an internal rib of the receiving hole is widened (elastically deformed) by the barrel tip inserted into the receiving hole. Therefore, the internal rib of the receiving hole tends to return to its original shape after the press-fit. With this, an inner wall surface of the receiving hole and a side face of the barrel tip of the outer barrel are in close contact with each other, whereby a closed space is formed between the receiving hole and the barrel tip of the outer barrel. At this point, a tip end of the puncture needle is not inserted into (does not reach) a bottom wall of the receiving hole. Therefore, the closed space is in communication with the atmosphere via the needle hole of the puncture needle and the inner space of the outer barrel. In other words, the closed space is not sealed.
The puncture needle and the barrel tip of the outer barrel are further inserted into the receiving hole, the tip end of the puncture needle is inserted into the bottom wall of the receiving hole, whereby the needle hole of the puncture needle is closed. Accordingly, the closed space is isolated from the atmosphere, and sealed.
The barrel tip of the outer barrel is then further inserted until the internal rib of the receiving hole is engaged with a portion where the outer diameter of the barrel tip of the outer barrel is reduced. As a result, the tip end of the puncture needle is further inserted into the bottom wall, and the cap is positioned to the barrel tip of the outer barrel due to an engagement between the internal rib of the receiving hole and the portion where the outer diameter of the barrel tip of the outer barrel is reduced, and friction resistance generated between the cap and the outer barrel.
As described above, the puncture needle and the barrel tip of the outer barrel are inserted into the receiving hole, and the cap is positioned to the barrel tip of the outer barrel, whereby the cap can be mounted detachably to the barrel tip of the outer barrel so as to seal the needle hole and the closed space. As a result, the puncture needle stored in the closed space can be protected from bacteria, and liquid (e.g., drug solution) can be filled between the inner space of the outer barrel and the plunger stored slidable in the inner space, in a liquid-tight manner. As described above, the process of mounting the cap to the barrel tip of the outer barrel includes a process of further inserting the barrel tip of the outer barrel into the receiving hole after the needle hole is closed to seal the closed space. In this case, gas remaining in the closed space with the sealed state is compressed by the barrel tip of the outer barrel inserted into the receiving hole. With this, the closed space has a positive pressure larger than the pressure around the cap (e.g., atmospheric pressure). Therefore, great force for further compressing the gas in the closed space against the positive pressure is needed to mount the cap to the barrel tip of the outer barrel.
Since the cap is mounted to the barrel tip of the outer barrel with the above positive pressure being generated, repulsive force is exerted between the cap and the barrel tip of the outer barrel in the direction in which the cap and the barrel tip are separated from each other. Due to this repulsive force, the cap is likely to be easily detached from the barrel tip of the outer barrel.
Especially when an assembly for a syringe is subject to a cleaning process, for example, the air around the assembly for a syringe is sucked for removing foreign materials, so that it is considered that the pressure around the cap is reduced and the positive pressure in the closed space is relatively increased. When an assembly for a syringe is sterilized with autoclave sterilization, or a sterilization method using sterilization gas such as ethylene oxide gas sterilization, or hydrogen peroxide gas sterilization, an inside of a sterilization device has to be depressurized before sterilization gas is supplied into the sterilization device having the assembly for a syringe inside. Therefore, pressure around the cap is reduced, and the positive pressure in the closed space is relatively increased. In the autoclave sterilization or ethylene oxide gas sterilization, the pressure in the sterilization device varies due to a volume fluctuation of gas caused by a temperature change, whereby it is considered that the positive pressure in the closed space becomes relatively larger than the pressure around the cap. When the positive pressure in the closed space becomes relatively larger than the pressure around the cap, the repulsive force increases to exceed friction resistance generated between the inner wall face of the receiving hole and the side face of the barrel tip of the outer barrel, resulting in that the cap might be detached more easily.